An important goal for researchers and pharmaceutical companies is to identify ways to use proteinaceous delivery vehicles to introduce novel molecules into the cytosol of cells, particularly into mammalian cells. Although there are a number of methods for the delivery of bioactive peptides and proteins into mammalian cells for therapeutic and biotechnological purposes, there is still a specific need for methods to deliver larger molecules, such as proteins, enzymes or cytotoxins, that cannot traverse the plasma membrane by a simple diffusive process.
The current technologies used to gain therapeutic access to the cytosol are limited in that they require large quantities of sample, have limited selectivity, and tend to not escape the intracellular endosome. Hence, efficient delivery of the novel therapeutics remains a hurdle in drug development.